This invention relates to a heat-sensitive transfer material which can give transferred recorded image of good printed letter quality even on a recording medium with poor surface smoothness.
With rapid progress of information industries, various information processing systems have been developed, and various recording methods and devices suited for the respective information processing systems have been developed and adopted. As one of such recording methods, the heat-sensitive recording method has recently been widely used because of various advantages such that the apparatus therefor is light in weight, compact, free of generating noise and also excellent in operability and maintenance.
However, of the recording papers used for the heat-sensitive recording method, ordinary heat-sensitive recording papers are expensive since they are converted papers containing a color forming agent and a developing agent, and also involve the problems that alteration of the recording is possible, that the recording paper is susceptible to color formation by heat or organic solvents and that the storability of the recording is poor with recorded image fading within a relatively short time.
As a method which maintains the advantages of the heat-sensitive recording method as described above and also compensates for the disadvantages with the use of heat-sensitive recording papers, the heat-sensitive transfer recording method is attracting attention.
The heat-sensitive transfer recording method employs a heat-sensitive transfer material, comprising generally a heat transferable ink containing a colorant dispersed in a heat-fusible binder applied by melting on a support in the form of a sheet. The heat-sensitive transfer material is superposed on the recording medium so that the heat-transferable ink layer may contact the recording medium, and the ink layer, melted by supplying heat through a thermal head from the support side of the heat-sensitive transfer material, is transferred onto the recording medium, thereby forming a transferred ink image corresponding to the pattern of the heat supplied on the recording medium. According to this method, the advantages of the heat-sensitive recording method as described above can be maintained, and also a plain paper can be used as a recording medium so that the above drawbacks accompanying the use of a heat-sensitive recording paper can be removed.
However, the heat-sensitive transfer recording method of the prior art is not free from drawbacks. That is, according to the heat-sensitive transfer recording method of the prior art, the transfer recording performance, namely the printed letter quality is greatly influenced by the surface smoothness, and therefore, although good quality of letter printing can be effected on a recording medium with a high degree of smoothness, the printed letter quality will be markedly lowered on a recording medium with a low degree of smoothness. However, even in the case of paper which is the most typical recording medium, a paper with high smoothness is rather special and the papers in general possess various degrees of concavities and convexities through entanglements of fibers. Accordingly, in the case of paper with a surface having a high degree of unevenness, the heated ink cannot penetrate into the fibers of the paper during transfer printing, but caused to adhere only at the convexities of the surface or in the vicinity thereof, with the result that the image printed at the edge portion is not sharp or a part of the image may be absent to lower the printed letter quality. For improvement of the printed letter quality, it may also be possible to use a heat-fusible binder having a low melting point. In this case, however, the heat transferable ink layer will have tackiness at a relatively low temperature to result in lowering storability or troubles such as staining at non-printed portions of the recording medium.